It can be done (it has been done), but there is a lot of modifying required to make it work.
Yep me too, I am not sure what part are identical.
But I think
spark plugs
air filter
seat
rear grab rail
front wheel
brake calipers
injectors
fuel filter
headlight/tail light
indicators
side covers
exhaust
rocker covers
coils
footpegs
oil filters
battery
I think I would get more joy from knowing what wasn't exchangeable!!
for example 500 heads on a 650?? will it fit
650 turbo on a 500?? will it fit
exhaust??
Frame??
rear shock?? I know the euro fits cos I've done it(1" shorter)
crank?
Food for thouught
Tone